Through the Telescope

by James Baikie

Chart of Mars. 'Memoirs of the British Astronomical Association,' Vol. XI., Part III., Plate VI.

Closely linked with the question of the existence of water on the planet, and indeed a fundamental point in the settlement of it, is the further question of whether there is any aqueous vapour in the Martian atmosphere. The evidence is somewhat conflicting. It is quite apparent that in the atmosphere of Mars there is nothing like the volume of water vapour which is present in that of the earth, for if there were, his features would be much more frequently obscured by cloud than is found to be the case. Still there are many observations on record which seem quite unaccountable unless the occasional presence of clouds is allowed. Thus on May 21, 1903, Mr. Denning records that the Syrtis Major (see Chart, Plate [XXI.]) being then very dark and sharply outlined, a very bright region crossed its southern extremity. By May 23, the Syrtis Major, 'usually the most conspicuous object in Mars, had become extremely feeble, as if covered with highly reflective vapours.' On May 24, Mr. Phillips observed the region of Zephyria and Aeolis to be also whitened, while the Syrtis Major was very faint; and on the 25th, Mr. Denning observed the striking whiteness of the same region observed by Mr. Phillips the day before. Illusion, so often invoked to explain away inconvenient observations, seems here impossible, in view of the prominence of the markings obscured, and the experience of the observers; and the evidence seems strongly in favour of real obscuration by cloud. It might have been expected that the evidence of the spectroscope would in such a case be decisive, but Campbell's negative conclusion is balanced by the affirmative result reached by Huggins and Vogel. It is safe to say, however, that whatever be the constitution of the Martian atmosphere, it is considerably less dense than our own air mantle.

During the last few years the public mind has been unusually exercised over Mars, largely by reason of a misapprehension of the terms employed in the discussion about his physical features. The talk of 'canals' has suggested human, or at all events intelligent, agency, and the expectation arose that it might not be quite impossible to establish communication between our world and its nearest neighbour on the further side. The idea is, of course, only an old one furbished up again, for early in last century it was suggested that a huge triangle or ellipse should be erected on the Siberian steppes to show the Lunarians or the Martians that we were intelligent creatures who knew geometry. In these circumstances curiosity was whetted by the announcement, first made in 1890, and since frequently repeated, of the appearance of bright projections on the terminator of Mars. These were construed, by people with vivid imaginations, as signals from the Martians to us; while a popular novelist suggested a more sinister interpretation, and harrowed our feelings with weird descriptions of the invasion of our world by Martian beings of uncouth appearance and superhuman intelligence, who were shot to our globe by an immense gun whose flashes occasioned the bright projections seen. The projections were, however, prosaically referred by Campbell to snow-covered mountains, while Lowell believed that one very large one observed at Flagstaff in May, 1903, was due to sunlight striking on a great cloud, not of water-vapour, but of dust.

As a matter of fact, Mars is somewhat disappointing to those who approach the study of his surface with the hope of finding traces of anything which might favour the idea of human habitation. He presents an apparently enticing general resemblance to the earth, with his polar caps and his bright and dark markings; and his curious network of canals may suggest intelligent agency. But the resemblances are not nearly so striking when examined in detail. The polar caps are the only features that seem to hold their own beside their terrestrial analogues, and even their resemblance is not unquestioned; the dark areas, so long thought to be seas, are now proved to be certainly not seas, whatever else they may be; and the canal system presents nothing but the name of similarity to anything that we know upon earth. It is quite probable that were Mars to come as near to us as our own moon, the fancied resemblances would disappear almost entirely, and we should find that the red planet is only another instance of the infinite variety which seems to prevail among celestial bodies. That being so, it need scarcely be remarked that any talk about Martian inhabitants is, to say the least of it, premature. There may be such creatures, and they may be anything you like to imagine. There is no restraint upon the fancy, for no one knows anything about them, and no one is in the least likely to know anything.

The moons of Mars are among the most curious finds of modern astronomy. When the ingenious Dr. Jonathan Swift, in editing the travels of Mr. Lemuel Gulliver, of Wapping, wrote that the astronomers of Laputa had discovered 'two lesser stars, or satellites, which revolve about Mars,' the suggestion was, no doubt, put in merely because some detail of their skill had to be given, and as well one unlikely thing as another. Probably no one would have been more surprised than the Dean of St. Patrick's, had he lived long enough, or cared sixpence about the matter, to hear that his bow drawn at a venture had hit the mark, and that Professor Asaph Hall had detected two satellites of Mars. The discovery was one of the first-fruits of the 26-inch Washington refractor, and was made in 1877, the year from which the new interest in Mars may be said to date. The two moons have been called Deimos and Phobos, or Fear and Panic, and are, in all probability, among the very tiniest bodies of our system, as their diameter can scarcely be greater than ten miles. Deimos revolves in an orbit which takes him thirty hours eighteen minutes to complete, at a distance of 14,600 miles from the centre of Mars. Phobos is much nearer the planet, his distance from its centre being 5,800, while from its surface he is distant only 3,700 miles. In consequence of this nearness, he can never be seen by an observer on Mars from any latitude higher than 69°, the bulge of the globe permanently shutting him out from view. His period of revolution is only seven hours thirty-nine minutes, so that to the Martian inhabitants, if there are any, the nearer of the planet's moons must appear to rise in the west and set in the east. By the combination of its own revolution and the opposite rotation of Mars it will take about eleven hours to cross the heavens; and during that period it will go through all its phases and half through a second display.

These little moons are certainly among the most curious and interesting bodies of the solar system; but, unfortunately, the sight of them is denied to most observers. That they were not seen by Sir William Herschel with his great 4-foot reflector probably only points to the superior defining power of the 26-inch Washington refractor as compared with Herschel's celebrated but cumbrous instrument. Still, they were missed by many telescopes quite competent to show them, and of as good defining quality as the Washington instrument—a fact which goes to add proof, if proof were needed, that the power which makes discoveries is the product of telescope × observer, and that of the two factors concerned the latter is the more important. It is said that the moons have been seen by Dr. Wentworth Erck with a 7⅓-inch refractor. The ordinary observer is not likely to catch even a glimpse of them with anything much smaller than a 12-inch instrument, and even then must use precautions to exclude the glare of the planet, and may count himself lucky if he succeed in the observation.

A word or two may be said as to what a beginner may expect to see with a small instrument. It has been stated that nothing under 6 inches can make much of Mars; but this is a somewhat exaggerated statement of the case. It is quite certain that the bulk of the more prominent markings can be seen with telescopes of much smaller aperture. Some detail has been seen with only 1¾-inch, while Grover has, with a 2-inch, executed drawings which show how much can be done with but little telescopic power. The fact is, that observers who are only in the habit of using large telescopes are apt to be unduly sceptical of the powers of small ones, which are often wonderfully efficient. The fine detail of the canal system is, of course, altogether beyond small instruments; and, generally speaking, it will take at least a 4-inch to show even the more strongly marked of these strange features. At the 1894 opposition, the writer, using a 3⅞-inch Dollond of good quality, was able to detect several of the more prominent canals, but only on occasions of the best definition. The accompanying rough sketch (Fig. 24) gives an idea of what may be expected to be seen, under favourable conditions, with an instrument of between 2 and 3 inches. It represents Mars as seen with a glass of 2⅝-inch aperture and fair quality. The main marking in the centre of the disc is that formerly known as the Kaiser or Hour-glass Sea. Its name in Schiaparelli's nomenclature, now universally used, is the Syrtis Major. The same marking will also be seen in Mr. Phillips's drawing of 1899, January 30, in which it is separated by a curious bright bridge from the Nilosyrtis to the North. The observer need scarcely expect to see much more than is depicted in Fig. 24, with an instrument of the class mentioned, but Plate [XX.] will give a very good idea of the appearance of the planet when viewed with a telescope of considerable power. The polar caps will be within reach, and sometimes present the effect of projecting above the general level of the planet's surface, owing, no doubt, to irradiation.

FIG. 24.

Mars, June 25, 1890, 10 hours 15 minutes; 2⅝-inch, power 120.